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July 2, 2012 -- Sexting is common among teens, with more than 1 in 4, or 28%, admitting they have sent a naked picture of themselves through text or email, according to new research.

If they had sent a naked photo, they were also more likely to be sexually active, the study shows.

"It may be a reliable indicator of actual sexual behavior," says researcher Jeff R. Temple, PhD, assistant professor of obstetrics and gynecology at the University of Texas Medical Branch Health in Galveston.

The study, which polled 948 public high school students, is published in the Archives of Pediatric and Adolescent Medicine.

Teen Sexting Study Details

Although the usual definition of sexting includes transmitting naked pictures as well as sexually explicit messages, usually over a cell phone, Temple, a psychologist, confined the definition in the study to naked pictures only.

The teens he surveyed were participating in his ongoing study, Dating It Safe.

They answered questions about transmitting naked pictures -- whether they had sent, asked someone to send, or been asked to send. If they had been asked, they told how bothered they were about it.

The teens ranged in age from 14 to 19, but ''the vast majority were 15 or 16," Temple says.

He also found:

31% said they had asked someone to send a naked picture.

57% said they had been asked to send a naked picture.

Of those who were asked, most said the request bothered them.

The teens also answered questions about sexual behavior, Temple says. Teens who sexted were more likely to report having engaged in sex.

Among girls, more than 77% of those who had sent a sext reported having had sex, compared to 42% of those who had not sent a sext. Among boys, nearly 82% of those who had sent a sext reported having had sex, compared to 45% of those who had not sent a sext.

Girls who engaged in sexting, but not the boys, had a higher chance of risky sexual behavior. For the study, that was defined as using drugs or alcohol before sex or having multiple partners.

Although Temple found no gender differences between the percentage who had sent a sext, the boys were more likely than the girls to ask for one. "Almost 70% of the girls had been asked," he says.

Which came first, the sexting or the sex?

"We can't answer that with this study," Temple says. "We are doing [new] studies hoping to get that sequence of events."

Previous studies on teens have found sexting rates ranging from 1% to 31%, according to Temple. However, much of that research is based on online surveys or studies with problems such as low response rates, he says.

Teen Sexting: Perspective

The new research adds some solid information about how common teen sexting is, says Megan A. Moreno, MD, MPH, MSEd, an assistant professor of pediatrics at the University of Wisconsin-Madison.

She wrote an editorial to accompany the study.

"I think sexting is still relatively new and there is a lot we don't know about it," she tells WebMD.

For pediatricians, the new research suggests that traditional questions about the use of media may need updating, she says.

Doctors often ask if there is a TV in the child's bedroom and if media are used for more than two hours a day, she says.

"Those questions are outdated," she says. "I think we [as doctors] need to replace and expand what we ask about."

Asking about social media use may help doctors step into conversations about sexual behavior with their teen patients, she says.

Moreno tells parents that sexting, for teens, may be part of their sexual experimentation. "This study helps to say, 'It does mean something -- your child may be more at risk for early sexual behaviors.'"

"Adolescents use social media to explore who they are or who they want to be," she says.

For parents, the new research ''is an in-your-face opportunity to either start or continue that discussion about your family's values and your thinking about sexual decision making."